1. Field of the Invention
The present invention relates to a method for forming a contact hole of a semiconductor device, and more specifically, to a method for forming a contact hole of a semiconductor device, wherein a contact hole is treated with a plasma of mixture gas containing oxygen to remove a polymer residual at the bottom of the contact hole for reducing contact resistance of a cell.
2. Description of the Prior Art
As the size of a cell is reduced due to high integration of a semiconductor device, it is critical to reduce the contact resistance of the cell.
FIGS. 1a through 1c are cross-sectional diagrams illustrating a conventional method for forming a contact hole of a semiconductor device.
Referring to FIG. 1a, a stacked structure of a conductive pattern 12 and a hard mask film 14 are formed on a semiconductor substrate 10. A nitride film (not shown) is formed on the entire surface of the resulting structure, and then blanket-etched to form a spacer 16 on sidewalls of the stacked structure of the conductive pattern 12 and the hard mask film 14. Thereafter, a capping layer 18 is formed on the entire surface of the resulting structure by depositing a nitride film, a carbide film or an alumina film.
Next, an interlayer insulating film 20 is formed on the entire surface of the resulting structure by depositing a BPSG (borophospho silicate glass) oxide film, a PSG (phospho silicate glass) oxide film, a TEOS (tetraethyl ortho silicate) oxide film, a PE-TEOS (plasma enhanced-tetraethyl ortho silicate) oxide film, an O3-TEOS (O3-tetraethyl ortho silicate) oxide film, a HDP (high density plasma) oxide film, an APL (advanced planarization layer) oxide film or a USG (undoped silicate glass) oxide film.
The nitride film, the carbide film or the alumina film which constitutes the capping layer 18 has selectivity over the oxide film which constitutes the interlayer insulating film 20.
Thereafter, a photoresist film (not shown) is formed on the interlayer insulating film 20, and then selectively exposed and developed to form a photoresist film pattern 22 which is a contact mask.
Referring to FIG. 1b, the interlayer insulating film 20 is selectively etched using the photoresist film pattern 22 as an etching barrier until the capping layer 18 is exposed to form a contact hole 24.
Thereafter, the residual photoresist film pattern 22 is removed using O2 plasma. The capping layer 18 at the bottom of the contact hole 24 is then etched using plasma of CF4/CHF3/Ar mixture gas or plasma of CHF3/O2/Ar mixture gas to expose an active region. An undesired polymer residual 26, which is an oxide film containing carbon or fluorine, remains at the bottom of the contact hole 24.
Then, the resulting surface is cleaned via a wet process using HF or 1OE (Buffered Oxide Etch, NH4F+HF) to remove the polymer residual 26.
The polymer residual 26 at the bottom of the contact hole 24 consists of complex film materials such as SixOyFz, SiXCy or SixOyNz. The oxide film of Si+, Si2+ or Si3+ still remains even after the cleaning process prior to a deposition of conductive layer material. The residual oxide film remaining at the interface of the active region and the conductive layer increases contact resistance, and cause a delay in a data read/write operation, which degrades characteristics of a device.
Therefore, the required time period for the cleaning process must be increased to remove the residual oxide film, which results in the damage of the interlayer insulating film 20, and insufficient margin of an isolation film for isolating contacts.
Moreover, since the oxide film of Si+, Si2+ or Si3+ may not be completely removed even when the time period for the cleaning process is increased, it is difficult to obtain a clean interface of the active region and the conductive layer.
Referring to FIG. 1c, a conductive layer 30 such as a polysilicon layer or a metal layer is deposited on the entire surface of the resulting structure, and then planarized to form a poly-plug or a metal line (not shown).